1. Field of the Invention
The invention generally relates to mechanisms for providing a selective hub to axle connection, and more specifically to a selectively lockable free-wheeling device for installation between a driven axle and a road wheel of a vehicle to be towed with its drive wheels on the ground.
2. Background Information
A road vehicle that is towed with all four wheels on the ground may incur damage to its transmission, a risk that is particularly severe in the case of cars having automatic transmissions. One approach to avoiding this problem is to install a free-wheeling device of some sort between a driven axle and at least one of the wheels. Those skilled in the vehicular arts will recognize that differential gearing of conventional sorts (i.e., non-limited slip) between the two wheels on a driven axle allows devices of this sort to be installed on only one of the two wheels on an axle. Moreover, although the disclosure herein is expressed in convention terms of xe2x80x9ca driven axlexe2x80x9d, those skilled in the vehicular arts will recognize that the same properties attributed to a driven axle are equally well attributable to a front wheel drive vehicle having two half-shafts comprising the equivalent of an xe2x80x9caxlexe2x80x9d.
An adapter mechanism of this sort, which allowed for conversion between a free-wheeling and a driven configuration was taught by the inventor in his U.S. Pat. No. 4,337,003, the disclosure of which is herein incorporated by reference. Although the arrangement taught in the inventor""s earlier patent allowed for conversion without having to remove the adapter mechanism or the road wheel, it did require changing wheel bolts. Short bolts were used to fasten the wheel to an outer flange of the adapter when in the free-wheeling configuration and longer, thinner bolts were used to attach the outer flange to the axle flange when the wheel was in the driven configuration.
In U.S. Pat. No. 4,610,558 Erickson described a self-contained adapter assembly that allowed a user to selectively place the attached road wheel into either of a driven or a free-wheeling configuration by turning a knob on the outboard end of the apparatus. The act of turning the knob caused two splined members in Erickson""s adapter to either engage for driving or to disengage for free-wheeled towing. Erickson placed his splined connectors, which had to sustain the driving torque applied to the road wheel when engaged, at the outboard end of his mechanism. In order for Erickson""s splined connection to be strong enough to sustain the torque it had to be relatively large, which increased the size of the surrounding hub sub-assembly enough that special wheels with oversize central openings sometimes had to be used when a small automobile was to be equipped with the adapter. The use of an increased central hole diameter can result in an unacceptably weakened road wheel.
In U.S. Pat. No. 4,453,852 Gilchrist discloses a hub disengaging apparatus for use on an agricultural machine having a power shaft that is axially shiftable between a driving position, in which the power shaft engages planetary transmission gears within a hub assembly, and a free-wheeling position that is selected when the machine is to be towed on a road.
When one of two drive wheels on an axle is moved outwardly by bolting an adapter between the vehicle""s wheel flange and the road wheel a tracking error is introduced. This offset can sometimes be compensated by installing either a second adapter or a dummy axle extension on the second side of the vehicle. In addition to tracking concerns, an adapter supplier must be concerned with the limited extent of axial outward displacement of a road wheel that can be made before encountering a significant problem of interference between a tire and a fender. In some prior art towing adapters the overall axial displacement is controlled by decreasing the axial distance between inner and outer adapter bearings, which increases side loads on the bearings and decreases their service life.
A preferred embodiment of the invention provides an adapter assembly for mounting on a road vehicle driving axle and for receiving a road wheel. This adapter assembly may be selectively set into one of a driving configuration and a free-wheeling configuration This preferred embodiment comprises a spindle, a hub, a spring-biased locking gear, a set of pushrods and an actuating member. The preferred spindle has a mounting flange at or near its inboard end and a shaft that has an axis extending substantially perpendicularly outboard from the mounting flange. The preferred shaft includes a splined portion adjacent the flange and an axially grooved portion outboard of the splined portion. The preferred hub is rotatably mounted on the spindle""s shaft and comprises a wheel flange for receiving a wheel and a sleeve having a splined portion along its inner surface. A spring fitting about the shaft and disposed between the flange and the splined portion of the shaft is used to bias an annular locking gear away from the flange. The preferred annular locking gear has a splined periphery for engaging a splined internal portion of the sleeve and a splined axial throughhole for engaging the splined portion of the shaft, so that the locking gear connects the sleeve to the shaft in the driving configuration when the splined periphery engages the sleeve and the splined throughhole engages the shaft. The preferred adapter also comprises at least two pushrods fitting into respective axial grooves in the shaft so that a respective inboard portion of each pushrod can be used to engage an outboard surface of the locking gear and so that a respective outboard end of each pushrod can be moved by a cam member that comprises a cam surface oblique to the axis of the shaft. The preferred cam member is mounted on the shaft for oscillation about its axis between a free-wheeling selection position, in which the cam surface does not push on the outboard ends of the pushrods, and a drive selection position, in which the cam surface engages the at least two pushrods and pushes them into engagement with the outboard surface of the locking gear so that the locking gear is urged into the driving configuration against the force of the spring.
A feature of a preferred embodiment of the invention is that the torque-sustaining portions of the apparatus are located between two bearings and are relatively close to the inboard end of the spindle. Because the outboard portions of the preferred apparatus do not have to sustain a wheel-driving torque, they can be smaller, so that the preferred apparatus can be used with substantially all standard vehicle road wheels without requiring the wheel to be weakened by having its central throughhole opened up. A particular preferred embodiment, for example, has an outer hub sleeve diameter of no more than 2xe2x85x9 inches.
Another feature of preferred embodiments of the invention is that although a portion of the shifting mechanism is adjacent to the outboard end of the spindle, much of the shifting mechanism is located closer to the inboard end of the spindle and in the space between two wheel bearings. This arrangement allows for relatively widely spaced bearings, which reduces end loading effects and is expected to increase the service life of the adapter apparatus beyond that characteristic of some prior art devices.
In some cases the towing adapter of the invention may be installed with a modified road wheel having a conical web that compensates for the axial offset introduced by the adapter. In particular, this may involve apparatus for mounting on an automobile driving axle, the apparatus comprising, in combination, a road wheel and an adapter assembly selectively set into either of a driving configuration and a free-wheeling configuration. The composite apparatus is characterized in that: the adapter assembly comprises a mounting flange for attachment to the driving axle and a wheel flange for attachment to the road wheel, where the mounting flange and the wheel flange are spaced apart by a predetermined axial distance. The road wheel comprises a flat annular portion for attachment to the wheel flange, a tire-receiving rim portion, and a conical web portion extending between the flat annular portion and the tire-receiving portion so as to provide the predetermined axial distance between the flat annular portion and a central plane of the rim, whereby the central plane of the rim is coplanar with the mounting flange when the road wheel is attached to the wheel flange.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.